1. Field of the Invention
The present invention relates aminothiol compounds which perform as superior catalysts in the asymmetric addition reactions of organic zinc and aldehyde.
2. Description of the Related Technology
For preparing secondary alcohols, one of the most important methods is to react organic zinc with aldehyde in addition reactions. In order to accelerate this reaction, chiral aminoalcohols are usually added as ligands to combine with organic zinc. Such chiral aminoalcohol create an asymmetric reaction environment, so that one of the produced chiral secondary alcohols is produced more than its stereoisomer, i.e., the asymmetric addition reactions. Apparently, the crux of obtaining a high chemical yield as well as enantioselectivity in the above reactions is to select proper chiral compounds which can provide excellent asymmetric environment for catalytical process.
Though many chiral compounds used in the addition reactions regarding organic zinc and aldehyde can achieve good enantioselectivity, however, these compounds have to be added at an amount at least 1% of the main reactants, and usually around 20%. Additionally, the enantioselectivity always decays with decreasing amount of the chiral ligands used. In general, the enantioselectivity is reduced below 90% enantiomeric excess (e.e.) when the chiral ligands are descended under 5%, so that most of above reactions are not good enough for industrial usage.
Aminoalcohols with optical activity, such as N,N-dibutylnorephe-edine, are frequently applied to accelerating the asymmetric addition reactions of organic zinc and aldehyde as chiral ligand catalysts. By adding aminoalcohols, enantioselectivity of the above reactions can be reached as high as 99% e.e., but an amount 10-20% of chiral aminoalcohols is need. Therefore, it's an important issue how to reduce the necessary amount of the chiral ligands used in the catalysis, so that it can be an economically efficient process